As the importance of magnetic disk drives used as storage devices of a large-sized computer, a workstation, a personal computer, and the like increases every year, such magnetic disk drives have been developed to have a large capacity and a small size. In order to realize such a magnetic disk drive having the large capacity and small size, high density recording is essential. For this reason, products using a perpendicular magnetic recording method are recently being developed for practical use since the high density recording is allowed in the perpendicular magnetic recording method unlike a known longitudinal magnetic recording method. For example, a magnetic recording medium using the perpendicular magnetic recording method has a layer configuration in which an adhesion layer, a soft magnetic layer, an intermediate layer, and a granular magnetic layer are stacked on a glass substrate or a rigid nonmagnetic substrate subjected to Ni—P plating on aluminum. In the case of the longitudinal magnetic recording method, the substrate is heated at a temperature of 200 to 400° C. in order to improve the magnetic properties. However, the magnetic properties of the granular magnetic layer used in the perpendicular magnetic recording method can be improved only below about 100° C.
Conventionally, a magnetic recording medium manufactured by using a film deposition technique based on sputtering is provided with a diamond like carbon (DLC) protective layer in order to protect a magnetic layer from sliding by a magnetic head, and the thickness thereof is 5 nm or less. In addition, in order to reduce friction between a magnetic head and a magnetic recording medium, it is common to coat a perfluopolyether liquid lubricant on the protective layer.
In general, the DLC protective layer may be obtained by depositing hydrocarbon radicals and hydrocarbon ions on a substrate by a chemical vapor deposition (CVD) method using hydrocarbon gas (for example, refer to Japanese Patent Publication No. 04-090125 “Patent Document 1”). In the case of a known longitudinal magnetic recording medium, since the temperature of a substrate is high as described above, hydrocarbon radicals, of which binding power is low and which have arrived at a surface of the substrate, are desorbed during film deposition using the CVD method and a sputtering effect occurs due to implantation of hydrocarbon ions. Thus, a DLC layer having high binding power can be generated as a protective layer remaining on a magnetic layer. In this case, as disclosed in Japanese Patent Publication No. 2004-152462 (“Patent Document 2”), the DLC protective layer has a hydrogen content of about 35% or less, and it is considerably preferable to reduce the hydrogen content in order to improve the flying ability of a magnetic head. Further, Japanese Patent Publication No. 2004-095163 (“Patent Document 3”) discloses a technique of realizing sufficient durability and making a film thin by using a two-layered carbon protective film including a plasma CVD carbon layer and a sputtered carbon layer.
However, for the perpendicular magnetic recording medium using the granular magnetic layer described above, hydrocarbon radicals are not easily desorbed since the temperature of a substrate is as low as 75° C. or less. In addition, since a DLC film, which cannot function as a protective layer due to poor binding power, or a very soft polymer like carbon (PLC) film is easily generated at the extremely high film deposition speed, it is difficult to protect a magnetic layer from shocks caused by a magnetic head and the corrosion resistance is not good. Furthermore, in this case, since the DLC film or the PLC film has a hydrogen content of 40% or more, the flying ability of the magnetic head also deteriorates.
In order to solve the above problems, Japanese Patent Publication No. 2006-114182 (“Patent Document 4”) discloses a technique of forming a satisfactory DLC film, which is excellent in sliding and corrosion resistance, using an effect of drawing hydrogen from a substrate reaction surface by mixing a hydrocarbon gas with a hydrogen gas and applying a bias voltage to a substrate.
A perpendicular magnetic recording medium disclosed in Patent Document 4 has a satisfactory DLC film excellent in sliding and corrosion resistance as a protective layer; however, since a Co-based alloy used for a recording layer of the perpendicular magnetic recording medium is susceptible to corrosion, it becomes difficult to obtain a result satisfying the product performance from the point of view of corrosion resistance and durability if the protective layer is made thinner in order to improve the recording density.